In our previous U.S. Pat. No. 3,867,939, we disclosed a disposable laminated pad for applying hot or cold therapy to a patient. This pad had two thermoplastic film panels secured together to define between them a circulating passage for hot or cold water. To an outer surface of this pad was secured a highly absorbent material, such as a soft paper of the quality used in facial tissue. Because the fibers of such absorbent material were not adequately anchored to the laminated plastic film conduit, it was necessary to incorporate a nonabsorptive grid, such as spun bonded nylon to an outer surface of the absorptive paper material or the like. This grid material was secured to the absorptive paper panel by laminating and partially melting a thin polyethylene film between the nonabsorptive grid and the absorptive paper. The purpose of the nonabsorptive grid material was to provide structural strength to the patient contacting surface of the medical pad. These pads often bear the full weight of the patient as he shifts his weight and moves about on the pad. When one recognizes that the absorptive material was similar to two layers of facial tissue, it is easy to recognize the requirement for the strong nonabsorptive grid material to protect the absorptive material, particularly when wetted for moist therapy.
Others have proposed various constructions for applying a soft comfortable patient contact surface on thermal pads. A typical approach is to use a slip cover over the pad, similar to putting a pillowcase over a hot water bottle. Some slip covers are sewn shut to permanently encase the heating pad. In heating pads which include water circulating tubes, opposite sides of the slip cover are sometimes stitched together with thread in an area between the circulating tubes.
U.S. Pat. No. 2,110,022 describes a covering for a thermal pad that is of cotton, linen, silk or the like. From the drawings and descriptions in this patent, this covering is believed to be of the pillow case slip cover construction described above. There is no mention of any surface to surface bonding of the cloth cover to the encased portions of the thermal pad. FIG. 3 of this patent shows a slight gap between the cloth covering and the encased portions of the pad. This patent fails to describe any securement of the cloth covering. If there were any securement, it would logically be by stitching with thread between the refrigerant circulating tubing. This is because large areas of the cloth covering lie against either a wool blanket 24 or loose cotton filling 32. A surface to surface bond between the cloth covering and these materials would be extremely difficult, making stitching by thread a logical choice, if indeed any securement of the cloth covering were desired.
Others have also proposed the pillow case or slip cover construction to thermal pads. In U.S. Pat. No. 2,250,325 a covering is secured by stitching 18. Also, in U.S. Pat. No. 3,211,216 a slip cover is shown stitched together at 13 between the encased refrigerant circulating tubing.
Another type of covering for a thermal pad was proposed in U.S. Pat. No. 2,726,658. In FIG. 3, a waterproof envelope of rubberized fabric is shown encasing the cooling liquid circulating tubing. This covering material would be inoperative for moist therapy because being "waterproof" it would repel rather than absorb water. This rubberized fabric envelope would have a construction similar to galoshes or rubberized workers' goves that begin with a cloth lining that is then rubber coated.